static int xmm_registers_available_p(void)
{
-#ifdef __GNUC__
- unsigned f;
- /* This hack is by Agner Fog. Use FXSAVE/FXRSTOR to figure out whether the
- * XMM registers are actually alive.
- */
- if (!cpuid_features_p(CPUID1D_FXSR, 0)) return (0);
-# if CPUFAM_X86
- __asm__ ("movl %%esp, %%edx; subl $512, %%esp; andl $~15, %%esp\n"
- "fxsave (%%esp)\n"
- "movl 160(%%esp), %%eax; xorl $0xaaaa5555, 160(%%esp)\n"
- "fxrstor (%%esp); fxsave (%%esp)\n"
- "movl 160(%%esp), %%ecx; movl %%eax, 160(%%esp)\n"
- "fxrstor (%%esp); movl %%edx, %%esp\n"
- "xorl %%ecx, %%eax"
- : "=a" (f)
- : /* no inputs */
- : "%ecx", "%edx");
-# elif CPUFAM_AMD64
- __asm__ ("movq %%rsp, %%rdx; subq $512, %%rsp; andq $~15, %%rsp\n"
- "fxsave (%%rsp)\n"
- "movl 160(%%rsp), %%eax; xorl $0xaaaa5555, 160(%%rsp)\n"
- "fxrstor (%%rsp); fxsave (%%rsp)\n"
- "movl 160(%%rsp), %%ecx; movl %%eax, 160(%%rsp)\n"
- "fxrstor (%%rsp); movq %%rdx, %%rsp\n"
- "xorl %%ecx, %%eax"
- : "=a" (f)
- : /* no inputs */
- : "%ecx", "%rdx");
-# else
-# error "I'm confused."
-# endif
+ int f = dispatch_x86ish_xmmregisters_p();
+
dispatch_debug("XMM registers %savailable", f ? "" : "not ");
return (f);
-#else
- dispatch_debug("GNU inline assembler not available; can't check for XMM");
- return (0);
-#endif
}
+ /* --- @rdrand_works_p@ --- *
+ *
+ *
+ * Arguments: ---
+ *
+ * Returns: Nonzero if the `rdrand' instruction actually works. Assumes
+ * that it's already been verified to be safe to issue.
+ */
+
+ #ifdef __GNUC__
+ static int rdrand(unsigned *x)
+ {
+ int i, rc;
+ unsigned _t;
+
+ i = 16;
+ __asm__ ("" : "=g" (_t));
+ __asm__ ("0: rdrand %2; jc 1f; decl %1; jnz 0b\n"
+ "mov $-1, %0; jmp 9f\n"
+ "1: movl %2, (%3); xorl %0, %0\n"
+ "9:"
+ : "=r" (rc), "+r" (i), "+r" (_t)
+ : "r" (x)
+ : "cc");
+ return (rc);
+ }
+ #endif
+
+ static int rdrand_works_p(void)
+ {
+ unsigned ref, x, i;
+
+ /* Check that it doesn't always give the same answer. Try four times: this
+ * will fail with probability %$2^{-128}$% with a truly random generator,
+ * which seems fair enough.
+ */
+ if (rdrand(&ref)) goto fail;
+ for (i = 0; i < 4; i++) {
+ if (rdrand(&x)) goto fail;
+ if (x != ref) goto not_stuck;
+ }
+ dispatch_debug("RDRAND always returns 0x%08x!", ref);
+ return (0);
+
+ not_stuck:
+ dispatch_debug("RDRAND instruction looks plausible");
+ return (1);
+
+ fail:
+ dispatch_debug("RDRAND instruction fails too often");
+ return (0);
+ }
+
#endif
/*----- General feature probing using auxiliary vectors -------------------*/